Imagine how different it'd be if luna and celestia weren't sisters. What if one of them were male, and not related. They could rule in love. But when one of them turns evil, the other banishes them, at the cost of their own heartbreak. But in the end they give birth to Cadence, who is the princess of love.

Also, since you seem to be aiming for a more realistic style with the wings than the show, here's a quick guide that may help if you want to make them look even better in the future: [link] (Yes, it's SFW.)